In some cases, the system needs to be downgraded to the previous version. The reason could be last known working version or new feature/settings not working as expected. Direct downgrade to wrong version will load the default configuration as the device will have no configuration to load.

Follow these steps to find out the last installed version,

1. Login as admin in CLI via ssh, or Console. Type shell sudo su - to go to shell ( you can directly login as root user in shell )

2. Navigate to upgrade backup directory,

    cd /var/upgradeBackup/

3. List the version upgrade files,

    ls -al | grep config

Here in above screenshot, the previous installed version is 6.0.10 so, the device can be downgraded to 6.0.10. 

Other installed versions can be seen too.